Neighbors add to a makeshift memorial in Phoenix. Police say loud barking dogs might have led to 56-year-old Michael Guzzo to kill four of his neighbors and the neighbors' two dogs before turning the gun on himself.

PHOENIX — It was the knock on the door every mother fears. Three police officers stood somberly to deliver the news.

“I’m sorry to tell you but Michael has been killed,” Jacque Alderman recalled one officer saying.

The 70-year-old’s son and three members of his family were shot to death over the weekend by a man neighbors say was incensed over the incessant noise of barking dogs.

For months, Michael Guzzo, 56, complained to neighbors about the barking from homes all around him in the tidy Phoenix complex where a central courtyard looks like a tree-laden park, even putting up fliers on doors advising people of pet ordinances and fines.

On Saturday, police say, Guzzo went on a rampage, methodically killing his neighbors Bruce Moore, 66; his daughter, Renee Moore, 36; her husband, Michael Moore, 42, who used his wife’s last name; and Renee’s son, Shannon Moore, 17, along with the family’s two dogs.

Guzzo then walked across the courtyard and tried to kill more neighbors who had dogs.

Libni Deleon, 26, said that just a few months ago he returned home from work to find Guzzo standing by his back gate where his two dogs were on the patio barking.

“He said, ‘Your dogs are barking. I’m here to live in peace,”’ Deleon recalled.

Moments after the killings Saturday, Guzzo went back to Deleon’s home and began kicking on the front door.

Libni Deleon’s wife, Vanessa, had just gotten out of the shower, grabbed their two children and ran upstairs to hide in the bathtub.

Libni went toward the door as Guzzo blasted two holes through it, sending about 20 shotgun pellets into the walls at the back of their home.

He ran upstairs to get his gun, opened the window and began to yell at Guzzo, who opened fire again before walking back to his own home to kill himself.

“I feel pretty darn lucky,” Libni Deleon said.

While Guzzo’s motive died along with him, neighbors and family members of the victims say he was becoming increasingly unhinged over dog noise.

“He hated them. But everyone here has dogs,” said Joni Flood, 27, who lives a few doors down from the victims.

Family members, meanwhile, struggled to come to grips with their loss, dumbfounded by the sheer senselessness of the killings.

Standing amid pools of drying blood on the home’s back patio where the two men were apparently shot first, Michael Moore’s brother called the killings “angering beyond belief.”

“It just angers me looking at all this because I just feel for my brother,” said Patrick Riley, 41. “The helplessness.”

The patio wall was chipped with pockmarks from the shotgun’s blast. Police haven’t given specific details of the attack.